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Balanced Fertilization — Real Benefits for Agriculture Sustainability

K.N. Tiwari & Rakesh Tiwari

Fertilizers feed the world by feeding the soils and in turn plants, and, if the world is not to go hungry, fertilizers will continue to play the key role in food production. No country in the world has been able to increase agricultural productivity without expanding the use of mineral fertilizers. In India, contribution of fertilizers towards increase in food grain production is estimated to be 50%. Farmers, their agricultural advisors, economists and policy makers all know this very well. What many seem less clear about is that simply adding some nutrients in excessive amount and ignoring the others altogether continuously is not only constraining crop production but the excessive use of any nutrient what the crop has already absorbed to capacity, is proving to be unproductive, expensive, wasteful and damaging to the environment. Simultaneously, utilization of those nutrients which were not replenished through external sources, in particular fertilizers, was mined causing severe nutrient deficiencies and thus constraining the crop productivity. So it is not so much ''fertilizer'' that feeds people but the ''balanced use of plant nutrients through external sources mainly fertilizers'' that will raise agricultural production and make more food available to a hungry world.

It has been estimated that fertilization accounts for nearly 50 per cent of all crop yield in India. In other parts of the world, where farm land has been abused for centuries or where new land is brought into production and quickly mined of its nutrients, fertilization might contribute as much as 75 per cent of total food production. Proper crop fertilization is essential to prevent massive global starvation. Herein, we should consider all the roles that soil plays in the production of food and fiber for the world's people. It is the medium in which plants grow and the source of most plant nutrients. Soil, water and air bathe plant roots and help keep them and above ground plant parts healthy and growing. The quality of soil in which plants grow is extremely important in determining yield as well as the sustainability of crop production. The key role of balanced used of fertilizers in maintaining soil fertility is well established. The present article deals with the real benefits of balanced fertilization for agriculture sustainability in India.

Balanced Fertilization Improves Soil Health: As science progressed, it was discovered that long term sustainability of crop production was dependent on building and maintaining soil fertility, an important soil quality measurement. Later, it was demonstrated that organic matter levels could be maintained and even increased through balanced fertilization. One of the greatest benefits of crop fertilization, aside from increasing crop yields and improving farmer profit, is its effect n soil organic matter. Harvested crop yields increase as a result of crop fertilization, as does unharvested plant biomass left on the soil surface and crop residues (roots) remaining in the soil. Most of the unharvested surface biomass and underground residues become soil organic matter positively influences structure, tilth, bulk density, water infiltration rates, water holding capacity, and water and air movement within the soil, thus improving soil quality. Organic matter helps to bind soil particles together, reduces soil crusting, increases the stability of soil aggregates, acts as a reservoir for plant nutrients, and reduces soil runoff and erosion losses.

Data from 12 long term experiments (LTE) conducted in India under the Indian Council of Agricultural Research (ICAR) Coordinated Project on Cropping Systems were analyzed to evaluate the effect of different sources of organic matter (farmyard manure (FYM) and green manure (GM)) in combination with inorganic fertilizer, on the productivity of rice wheat systems. The fertilizer treatments showed no significant effect on final yield, although the initial yield was significantly higher with 100% NPK than with FYM. The average rice yield with 100% NPK was still significantly higher than with FYM. In wheat, average yields and yield trends were not significantly different among the fertiliser treatments.

Other long term rotation studies in India have also demonstrated that moderate amounts of fertilizers increase soil organic matter quantity and quality. The positive benefits of fertilization have been directly attributed to the amount of crop residues returned to the soil. In addition to higher grain yields, fertilizer increased straw and root production, the precursors of soil organic matter. However, the realities surrounding short supplies of FYM because of burning of cow dung for fuel and the high labour and transportation costs continue to restrict its extensive and widespread application in agriculture. It is most likely that the most immediate solution to sustaining crop yields in the absence of adequate FYM supply will come from the regular use of site specific application of inorganic fertilizers.

Balanced Beyond NPK

Balanced fertilizer use today implies much more than NPK application. In India, almost 50 per cent of over 200,000 soil samples analyzed have tested low (deficient) in zinc. Soil S deficiencies once considered to be confined to coarse textured soils under oilseeds are now estimated to occur in a wide variety of soils in close to 130 districts and S induced yield increases under field conditions have been recorded in over 40 crops. Likewise, in specific areas, the application of magnesium (Mg) and boron (B) has become necessary for high yields, greater nutrient use efficiency and enhanced profits. These nutrient combination represent the many facets of balanced fertiliser use (Table 1).

Table 1. Balanced nutrient application for a number of soil/crop combinations in India

No.

Situation

Component of Balance

1

Alluvial soils, rice-wheat belt

N, P, K, S, Zn and B

2

Red and lateritic soils

N, P, K, S, B with lime

3

Areas under oilseeds

N, P, K. S, Zn and B

4

Man land area of Karnataka

N, P, K, S and Mg

5

High yielding tea in South

N, P, K, Mg, S and Zn

Source : Tiwari (2000)

Therefore, feeding crops for high yields in India is no longer a simple NPK story. This is no way minimizes the importance of NPK (fertiliser pillars) but emphasizes that the efficiency of NPK and returns from their application can be maximized only when due attention is also paid to other nutrient deficiencies.

Table 2. Effect of balanced (NPK) fertilization on agronomic efficiency of nitrogen (AEN)

Crop

Control yield (kg ha-1)

N applied (kg ha-1)

AEn

Increase in AEn (%)

N alone

+ PK

Rice (wet season)

2,740

40

13.5

27.0

100

Rice (summer)

3,030

40

10.5

81.0

671

Wheat

1,450

40

10.8

20.0

85

Pearl millet

1,050

40

4.7

15.0

219

Maize

1,670

40

19.5

39.0

100

Sorghum

1,270

40

5.3

12.0

126

Sugarcane

47,200

150

78.7

227.7

189

Source : Prasad (1996)

Balanced Fertilization Improves Nutrient Use Efficiency (NUE) : Research has shown that when N is balanced with P, K and other essential plant nutrients, N use efficiency increases. That means more N is used by the crop and less is left in the soil as a potential pollutant. Thus, efficiency of applied N depends not only on the N applied, but also on the availability of other nutrients. When balanced fertilization is practiced, one nutrient often increases the efficiency of the other through synergistic interaction. Data from a large number of multi location experiments conducted under the ICAR's LTE project, and on farmer's fields under the AICARP, clearly bring out the importance of balanced fertilization in increasing NUE (Table 2).

 
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